Air filters are routinely provided in central heating and air conditioning systems of office and residential buildings. These filters commonly employ non-woven, polyester fiber, air filtration media to filter dust type airborne particulates of sizes in excess of 10 microns from the air. Today the media often is treated with antimicrobial agents to rid air of fungi, bacteria, viruses, algae, yeasts and molds. This conventional air filtration media is not washable and thus has to be periodically replaced. Its effectiveness in ridding air of microorganisms has also been very limited since the fibrous media is so lacking in density as to permit a significant portion of submicron sized particles and air at the molecular level to pass through the media without direct contact with the treated fibers.
In some spatial environments it is necessary to filter submicron particulates from the air with far greater efficiency. Industrial clean rooms and hospital surgical rooms, for example, require that particulates as small as some 0.1 microns be filtered in a highly efficient manner. For this purpose high efficiency particulate arresting filters, commonly referred to as HEPA filters, are employed. HEPA air filtration media is usually in the form of pleated sheets of paper comprised of a random matrix of borosilicate micro fibers. The individual pleats may be separated by metallic separators or made separatorless by the media itself being formed with embossed areas or dimples. HEPA media is so dense however, particularly when the pleats have been tightly compacted, as to require the use of air blowers and fans more powerful than those employed in conventional central air conditioning and heating systems. HEPA filters have therefore been believed to be unsuitable for use in central air heating and air conditioning systems, particularly if treated with an antimicrobial agent, or combined with additional filters, without enhancement of their airflow driving means.
Another type of air filtration media, which is washable and reusable, is thermally reticulated polyester or polyurethane foam. This media is today used to filter airflow in internal combustion engines such as those used to propel automobile vehicles and lawn mowers. It is effective in filtering dust-like airborne particulate larger than 10 microns. However, it has been believed not to be useable in central heating and air conditioning systems.
Still another type of air filtration media is that of fibrous non-woven polyester and polyurethane sheets impregnated with activated carbon. This media is useful in deodorizing air as odor generating molecules entrained in airstreams attached to particulates filtered by the fibers migrate into the carbon pores where they become entrapped. Attempts to apply antimicrobial agents to this type of media have failed as the agents have been found to deactivate the carbon particles.
As previously stated, microorganisms such as fungi and bacteria are too small to be filtered by disposable, non-woven, polyester fiber media or by reusable, thermally reticulated polyester and polyurethane foam filter media. For example, the rod length of acetobacter melanogenus is between 1.0 and 2.0 microns; that of bacillus anthraces between 3.0 and 10.0 microns; that of haemophilus influenzae between 0.5 and 2.0 microns; that of shigella dysenteriae between 1.0 and 3.0 microns; and that of streptococcus lactis between 0.5 and 1.0 microns. Indeed, the average size of such bacteria is one-half micron. The air ducts of buildings in which people have been stricken with the illness now known as sick building syndrome have been treated with antimicrobial agents but with only very limited and quite temporal effectiveness. And, as previously stated, attempts to treat the filter media itself have failed to be effective without airflow enhancements.
It thus is seen that a need has long existed for an air filter capable of being used in conventional central heating and air conditioning systems of office or residential buildings that is effective in ridding the air of microorganisms without the need for stronger air circulation means. It is therefore to the provisions of such that the present invention is primarily directed.